The present invention is related to blown optical fiber. In particular, it is related to a penetrator and method for passing blown optical fiber through a pressure-proof boundary.
The method and apparatus for blowing optical fiber into ducts are well known. The method entails constructing an optical fiber duct circuit using duct designed for this purpose. Optical fiber is then blown from one point in the circuit to another using a special blow head. Depending on the desired application, more than one optical fiber may be blown through the duct at the same time.
In some instances, it is necessary to carry the optical fiber circuit through a pressure-proof boundary. When this is the case, it is important to ensure that the optical fiber circuit does not become a pathway for leakage across the boundary.
Several methods for passing optical fiber through pressure-proof boundaries have been described in U.S. Pat. Nos. 5,588,086; 4,214,809; 3,825,320; 3,951,515; 4,767,173; and 5,155,795 which are incorporated by reference herein. None of these methods make it possible to blow optical fiber(s) through a penetrator. Either each optical fiber is passed singly through the penetrator or the fiber itself does not actually cross the pressure-proof boundary. In some instances, the signal is carried across the boundary by a glass medium. When the penetrator is employed, the opening in the pressure-proof boundary must be as large or larger than the part that carries the optical fiber, or that carries the signal. This is in contrast to the present invention, where the fiber/signal carrying part has the same cross-sectional area as the opening in the boundary. Therefore, with respect to pressure vessels, the opening in the boundary may be smaller than or no larger than the maximum opening requiring reinforcement yet it may permit one to a plurality of fibers to be blown across the boundary.
U.S. Pat. No. 4,682,846 discloses a penetrator where the opening in the boundary is about the same size as the optical fiber. A glass plug forms the pressure boundary in this penetrator. In turn, the optical fiber does not cross the boundary and the penetrator cannot be used for blowing an optical fiber or multiple fibers. Also, because the boundary is glass, the amount of pressure that can be sustained by the plug coupled with the durability of the seal under hard use conditions is questionable. The present invention overcomes these problems and offers other advantages such as permitting easy upgrading through replacement of some of the penetrator parts and blowing new optical fibers while maintaining the integrity of the boundary. In addition, the invention does not employ exotic or expensive parts, materials, or manufacturing processes. Rather the invention offers an inexpensive, and efficient installation method and equipment.
The present invention is a penetrator for passing blown optical fiber through a pressure-proof boundary. The penetrator comprises a cylinder for attachment substantially in line with an opening in the boundary. The cylinder has a proximal and a distal end cap, a cylinder wall, and a central passage or dip tube for optical fibers. The central passage has substantially the same cross-sectional area as the opening in the boundary. The dip tube is sealed to each end cap and has distal and proximal tee fittings for injecting sealing materials into the dip tube. The tee fittings are joined by a length of optical fiber duct therebetween.
In use, the proximal end cap of the penetrator is attached to the boundary in line with an opening in the boundary. An optical fiber duct circuit is attached to the side of the boundary opposite from the proximal end cap and in sealing relationship with the opening in the boundary. An optical fiber duct is attached to the distal tee fitting to complete an optical fiber duct circuit. Optical fiber is blown through the optical fiber duct circuit to a terminal. A damming material is injected into the distal tee fitting and a sealing material is injected into the proximal tee fitting to fill the central passage or dip tube.
The objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be obtained by means of instrumentalities in combinations particularly pointed out in the appended claims.